JP2698494B2 - Image heating device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image heating apparatus for heating an image on a recording material, and more particularly to an image heating apparatus suitable for heating and fixing an unfixed image on a recording material.

[0002]

2. Description of the Related Art As an image heating apparatus for heating and fixing an unfixed image and improving the surface properties of an image, a heat roller system in which a heating roller and a pressure roller sandwich and convey a recording material supporting an image is widely used. doing.

In such a heat roller system, the core of the heat roller is becoming thinner in order to increase the heating rate of the heat roller.

[0004] Also, Japanese Patent Application Laid-Open No. 63-313182,
Japanese Patent Application Laid-Open No. 2-157878 discloses a heat fixing device using a thermal head having a low heat capacity and a film sliding on the thermal head.

This heat fixing device has an energizing heat generating layer extending in a direction perpendicular to the moving direction of the recording material, and energizes the entire energizing heat generating layer regardless of the size of the recording material.

[0006]

In an image heating apparatus using a heating roller or a thermal head having a very thin cored bar, the temperature of the non-sheet passing portion is increased outside the width of the recording material.

Particularly, when a recording material having a width smaller than the maximum size is continuously passed, the temperature rise in the non-sheet passing portion is large.

If the temperature rise in the non-sheet passing portion becomes large, the image heating device becomes abnormal, deteriorates, or is damaged in severe cases.

Further, in the above-described image heating apparatus using a film, a large temperature difference between a paper passing portion and a non-paper passing portion causes wrinkles and meandering of the film.

[0010]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a heating element provided in a direction intersecting a moving direction of a recording material for heating an image on a moving recording material; A first thermistor provided in the minimum recording material passage area for detecting the temperature of the heating element, and energization control means for controlling energization of the heating element so that the detected temperature of the first thermistor maintains a target temperature And a second thermistor outside the minimum recording material passage area. When the second thermistor detects a predetermined first temperature during continuous image heating, the recording material feeding interval is increased. When a predetermined second temperature higher than the first temperature is detected, the feeding of the recording material is stopped.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 shows a schematic configuration of an example of an image forming apparatus using the fixing device 60 according to the embodiment of the present invention.

The image forming apparatus of this embodiment is an electrophotographic copying apparatus of a document table fixed-optical system moving type, a rotating drum type, and a transfer type.

After the original 19 is placed on the fixed original platen glass 20 as required and the necessary copy conditions are set, when the copy start key is pressed, the photosensitive drum 39 is rotated clockwise in the direction indicated by the arrow. It is driven to rotate at the speed.

The light source 21 (22 is a reflection shade) and the first mirror 23 move forward along the lower surface of the original table glass 20 from the home position on the left side of the glass to the right side of the glass at a predetermined speed V. When the third mirrors 24 and 25 move in the same direction at a speed of V / 2, the downward image surface of the placed document 19 on the platen glass 20 is illuminated and scanned from the left side to the right side, and the illumination is performed. The scanning light reflected from the document surface is imagewise exposed (slit exposed) to the surface of the rotating photosensitive drum 39 via the image forming lens 29 and the fixed fourth to sixth mirrors 26, 27 and 28.

The surface of the rotating photosensitive drum 39 is uniformly charged to a predetermined positive or negative potential by the primary charger 30 before the exposure, and the above-described exposure is performed on the charged surface. Thus, an electrostatic latent image having a pattern corresponding to the original image is sequentially formed on the surface of the drum 39. Photosensitive drum 3
The formed electrostatic latent images on the nine surfaces are visualized as toner images by the developing roller 32 of the developing device 31.

On the other hand, a transfer material sheet P as a recording material is fed by a paper feed roller 61, passed through a guide 33, and introduced at a predetermined timing to a transfer portion between a drum 39 and a transfer charger 34 to be transferred. Drum 39 by receiving corona
, And the toner visible image on the drum 39 side is sequentially transferred to the sheet P side.

The sheet P that has passed through the image transfer section is discharged
While being subjected to the charge removal of the back surface charge, the toner is sequentially separated from the surface of the drum 39, is introduced into the fixing device 60 by the transport unit 38 and the entrance guide 10, receives the toner image fixation as described later, and receives And a pair of discharge rollers 40
Is discharged out of the machine.

The surface of the drum 39 after the transfer is the cleaning device 3
The cleaning blade 37 of No. 6 removes stains such as residual toner and cleans the surface, and is repeatedly used for image formation.

When the moving optical members 21 to 25 have reciprocated, when they reach the predetermined forward end point, they are turned to the backward movement, return to the first home position, and wait for the start of the next copy cycle (back stroke of the optical system). ).

If a plurality of copies (for example, 100 copies) are designated before the copy start key is pressed,
After the back process of the optical system is completed, the above-described steps are repeated at predetermined intervals by the microcomputer MPU shown in FIG. 3 to continuously form an image.

Next, a fixing device 60 which is an image heating device according to an embodiment of the present invention will be described.

FIG. 1 is a side sectional view of the fixing device 60.

Reference numeral 6 denotes an endless belt-shaped fixing film, which includes a driving roller 7 for rotating and driving the fixing film on the left side in the figure, a driven roller 8 for driven rotation by the fixing film on the right side, and a gap between the two rollers 7 and 8. A low-heat-capacity linear heater 1 fixedly disposed below is suspended between three members 7, 8, and 1.

The driven roller 8 also serves as a tension roller for applying tension in a direction in which the fixing film 6 is stretched outward.

The fixing film 6 is covered with a rubber layer of silicon rubber or the like on its surface to increase the coefficient of friction. It is driven to rotate without delay.

Reference numeral 9 denotes a pressure roller having a rubber elastic layer having good releasability, such as silicon rubber, as pressure means for applying pressure between the heater, the fixing film, and the recording material. The film 6 is sandwiched between the heater 1 and is pressed against the lower surface of the heater 1 by a biasing means such as a spring with a contact pressure of, for example, a total pressure of 5 to 10 kg. Then, it rotates counterclockwise in the figure, which is the forward direction.

The endless fixing film 6 which is driven to rotate is repeatedly provided for the heat fixing of the toner image, so that it has excellent heat resistance, releasability and durability.
A thin film having a thickness of not more than μm, preferably not more than 40 μm is used. As an example, the outer peripheral surface of a high-heat-resistant resin such as polyimide, polyetherimide, polyethersulfone, or polyetheretherketone having a thickness of 20 μm, or a thin-walled endless belt made of metal such as nickel or SUS is coated with PTFE.
(Tetrafluoroethylene resin), PFA (tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer resin)
Resin having a low surface energy, or a releasable coating layer obtained by adding a conductive material such as carbon black to these resins.
This is an endless belt having a total thickness of 30 μm and a thickness of 0 μm.

The heater 1 having a low heat capacity has, for example, a thickness of 1.
A heat generating layer 3 is formed by coating a resistance material such as silver palladium ruthenium oxide to a thickness of 10 μm and a width of 1.0 mm on a highly heat conductive alumina substrate 2 having a thickness of 0 mm, a width of 10 mm and a length of 340 mm. 10 μm thick film 6 on top
The protective layer 4 is made of glass or the like in consideration of sliding with the heater support 11 and is fixedly supported by being attached to and held by the heater support 11.

The heater support 11 has a heat insulating property, a high heat resistance and a rigidity for thermally supporting the heater 1 with respect to the fixing device 60 and the image forming apparatus, and includes, for example, PPS (polyphenylene sulfide) and PEEK (polyether). (Ether kettle), high heat-resistant resins such as liquid crystal polymers, and composite materials of these resins with ceramics and metals.

Electric power is supplied to the heating layer 3 of the heater from both ends in the longitudinal direction.

The current is supplied at an alternating current of 100 V, and the temperature detected by a temperature detecting element 5 such as an NTC thermistor, which is adhered to or pressed against the back surface of the substrate 2 with a thermally conductive silicon adhesive or the like, is maintained at a predetermined constant temperature. The energization control is performed by the microcomputer MPU13 (FIG. 3) so that the power is supplied.

FIG. 3 is a side view of the heater 1 as viewed from the paper feeding side. The heat generating layer 3 that generates heat by energization is formed substantially in the center of the lower surface of the substrate 2 in a straight line along the length of the substrate.
Reference numerals 3a and 3b denote current-carrying electrodes (input terminals) made of a good conductive material such as silver provided on the left and right ends of the heat generating layer 3.

E is the effective total length of the heat generating layer 3 between the electrodes 3a and 3d. In this embodiment, the maximum size transfer material sheet which can be supplied to the apparatus and used is a length corresponding to the A3 plate (width 297 mm). It is set to the size.

In the image forming apparatus shown in FIG. 2, transfer material sheets of various sizes are supplied on a so-called one-side basis with respect to a base line A on the left end side of the heat generating layer 3.

The paper passing area C of the A6 plate (width 105 mm) is shown in FIG.
Is a sheet passing area of a recording material of the minimum size usable in the image forming apparatus shown in FIG.

5A is a thermistor which is a temperature detecting element provided in the minimum sheet passing area.

At the time of fixing, the MPU 13 controls the heater drive circuit 14 so that the detection output of the thermistor 5A becomes a predetermined constant value, and controls the energization to the heat generating layer 3.

Reference numeral 5B denotes a thermistor which is a temperature detecting element provided outside the minimum sheet passing area. In this embodiment, the thermistor is disposed inside the maximum sheet passing area e and further outside the B4 plate (257 mm width) sheet passing area d. is there.

Next, the fixing operation of the first sheet will be described.

After the image forming apparatus starts the image forming operation according to the image forming start signal, the rotation of the fixing film 6 and the energization to the heater 1 are started at a predetermined timing.

A transfer material sheet P carrying an unfixed toner image T on the upper surface, which is a recording material, is conveyed from the transfer unit 34 to the fixing device 60. The sheet P is guided by the entrance guide 10 and rapidly heated to the predetermined fixing temperature, and enters the pressure contact portion N between the pressure roller 9 and the unfixed toner on the heater side in close contact with the fixing film 6. I do.

The sheet P is overlapped with the movable fixing film 6 without causing surface deviation or wrinkling, and the heater 1
It passes through a fixing nip portion N between the pressure roller 9 and the pressure roller 9 while receiving a clamping force.

The toner image carrying surface of the sheet P receives the heat of the heating element 3 via the fixing film 6 while passing through the fixing nip portion N in a state of being pressed and adhered to the fixing film surface, so that the toner image is melted at a high temperature. To soften and adhere to the surface of the sheet 6.

In the case of the apparatus of this embodiment, the sheet P as the recording material and the fixing film 6 are separated from each other when the sheet P passes through the fixing nip N.

At the time of this separation, the temperature of the molten toner Ta is still higher than the glass transition point of the toner.

Since the toner Ta at a temperature higher than the glass transition point at this separation point has an appropriate rubber property, the toner image surface at the time of separation has an appropriate uneven surface property without following the fixing film surface. As a result, the surface properties are maintained, and the solidified particles are cooled and solidified. Therefore, the fixed toner image surface does not have excessive image gloss and has high image quality.

The sheet P separated from the fixing film 6 is guided by the paper discharge guide 12, and the temperature of the toner Ta higher than the glass transition point naturally falls (natural cooling) while reaching the paper discharge roller pair (40). As a result, the temperature becomes equal to or lower than the glass transition point and the solidification Tb is reached, and the sheet P on which the image is fixed is output.

Next, an operation sequence during continuous image formation will be described.

FIG. 4 shows the ON timing of the image formation start signal when a plurality of (for example, 100) copies are set before the copy start key is pressed, and the sheet P passes through the fixing nip N. Timing ("Yes"
When the sheet P is passing, when nothing is not passing)
And two timing chart of a detected temperature T and diagrams are also shown at the same time axis graph showing the time change of the detected temperature T ₂ of the second thermistor 5B of the first thermistor 5A.

The image forming start signal of the present embodiment is a signal from the microcomputer MPU 19 for starting the operation of the unillustrated clutch and the light sources 21 and 22 for controlling the operation of the sheet feeding roller 61, and performs the first image forming operation. It is a signal to make it.

In this example, B4 size (257 m width)
m) with a sheet weighing 80 g / m ² at a speed of 100 m
Paper is passing at m / sec. Further, in the present embodiment is kept at a fixing temperature T ₁ of the detected temperature T ₁ is constant in the first thermistor 5B '(e.g. 190 ° C.), a predetermined power corresponding to the value of T ₁ is supplied to the heater 1 You. At the same time when the copy key is pressed at time τ ₀ , an image formation start signal is transmitted from the MPU 19 to each section of the image forming apparatus. For example, the sheet feed roller 61 starts rotating and the sheet P is conveyed toward the transfer charger 34. At the same time τ ₀ , rotation of the film 6 of the fixing device and energization of the heater 3 are started.

At time τ ₁ , the sheet P having a width of B4 reaches the fixing point P, but by then, the thermistor detection temperatures T ₁ and T ₂
From the room temperature to T ₁ ′ at substantially the same speed. While the sheet P passes through the nip N, T ₁ = T ₁ ′, but T ₂
Rises from T ₁ ′ due to the so-called non-sheet passing portion temperature rise.

After staying at the nip N for a time t _c (= τ ₂ −τ ₁ ), the sheet exits the fixing nip N.

The MPU 19 generates a second image forming signal after a time t ₀ (for example, 5 sec) from the start of the copy key, and feeds the sheet P. Then, the second sheet enters the nip N at time τ ₃ with an interval of a predetermined time t _i after the first sheet passes through the nip N. Thereafter, the above operation is repeated for a while.

The second thermistor detection temperature T ₂ increases during the sheet passing period t _{c and} decreases during the interval period t _i .
Looking at the macro, it gradually rises.

[0057] The second thermistor 5B at the time before the next 54th image formation signal after time tau ₄ 53 th image forming signal emitted is emitted _{τ 5 (τ 5 <τ 4} + t 0) the detection temperature T ₂ at a predetermined temperature T ₂ '(this example 240
° C).

[0058] Thus non-sheet passing portion is raised, the temperature detected by the second thermistor 5B of the non-sheet passing area is than the fixing temperature T ₁ 50
When the temperature rises above T ₂ ′, the microcomputer MPU
Numeral 13 increases the interval during continuous image formation.

That is, the image forming signal is not generated even when the time t ₀ elapses from the time τ ₄ , and the time τ _{6 obtained} by further adding the time t _i.
At (τ ₆ = τ ₅ + t ₀ + t _i = τ ₅ + t _c + 2t _i ), the 54th sheet image forming signal is issued. Then, the interval of the sheet P entering the fixing nip is t _i for the 1st to 53rd sheets, but it is doubled to 2t _i between the 53rd and 54th sheets. Thereafter, until the 100th image formation, the MPU1
9, the interval of the image formation start signal is t ₀ ′ = t ₀ +
t _i , longer than the initial. Therefore, the difference in heat radiation amount of the heat radiation amount and the first thermistor position of the second thermistor position per unit time in the heater surface is smaller than initially, thus the second thermistor temperature T ₂ is reduced. That is, the temperature rise in the non-sheet passing portion is reduced.

[0060] Except the point COMPARATIVE EXAMPLE is always t ₁ without changing the paper feeding interval were performed continuous copying of 100 sheets in the same manner as described above in Example.

At the 100th sheet, T ₂ = 260 ° C.
Then, the film was displaced to the higher temperature side, and the edge of the film was damaged. Further, when the 100 copies were repeated 20 times (total 2000 copies), the coating of the fixing film was damaged.

[Embodiment 2] FIG. 5 is a timing chart of a second embodiment of the present invention.

The number of copies was set to 150 before pressing the copy start key.

The viewpoint temperature T ₂ of the second thermistor 5 B increases as the number of continuous copies advances, and reaches T ₂ ′ (260 ° C.) at the 53rd sheet as in the first embodiment.

Therefore, the interval is t ₁ after the 54th sheet.
Non-sheet-passing portion temperature detected by the 54 th and subsequent second thermistor by extending 2t ₁ is reduced from.

At time T ₇ , which is less than t ₀ ′ after the 99th image forming signal is issued at time T ₆ , the detected temperature T ₂ ≦ T ₂ ″ <T ₂ ″ = 220 ° C. of the second thermistor 5B. T ₂ ′).

As described above, the second thermistor 5B in the non-sheet passing area
When the detected temperature is sufficiently lowered and becomes equal to or lower than the fixing temperature but sufficiently lower than the temperature T ₂ ″ at which the apparatus has room, the microcomputer MPU 19 again shortens the interval at the time of continuous image formation and returns the interval to t _i .

As a result, the 101st image forming signal is τ ₉
= Τ ₈ + t _o (= τ ₈ + t _c + t _i ).

[0069] The image forming signal in a subsequent interval t _o is on.

After the 100th sheet P has passed through the nip,
The value of T ₂ starts to rise again. 'The interval of re-image formation start signal When you become a t _0' again T ₂ is _{T 2 ≧ T 2 = t o} + t
Extend to _i .

According to the present embodiment, the number of copies per unit time can be increased compared to the first embodiment, while preventing damage due to the temperature rise of the non-sheet passing portion.

[Embodiment 3] In the first and second embodiments, the interval is switched between two stages of t ₁ and 2t ₁ .
In this embodiment, the switching is performed in more detail.

FIG. 6 shows the relationship between T ₂ and the interval in this embodiment.

Until the detected temperature T ₂ of the second thermistor 5 B reaches T ₂ ″ (220 ° C.), continuous copying is performed at intervals t _i .

When T ₂ ″ ≦ T ₂ <T ₂ ′ (240 ° C.), the interval is

[0076]

[Outside 1] And the interval is 2t when T ₂ ′ ≦ T _{2
Increase i} and 100%.

However, the temperature in the non-sheet passing area still continues to rise, and T ₂ =
When the temperature reaches T ₃ (260 ° C.), the apparatus is stopped.

According to this embodiment, it is possible to achieve both prevention of the temperature rise in the non-sheet passing portion and reduction in the number of copies per unit time.

In this embodiment, the interval is switched between three steps, but may be switched more finely or steplessly.

[Embodiment 4] The degree of temperature rise in the non-sheet passing portion differs depending on the sheet passing size, particularly the distance from the sheet passing end.

Therefore, in this embodiment, the size of the recording material is detected by size detecting means (not shown), and the value of the temperature T ₂ ′ for changing the paper passing interval during continuous image formation in accordance with the detected size of the recording material. Switch.

That is, T ₂ ′ = 240 ° C., A
T ₂ ′ = 235 ° C. for 4 passes, T ₂ ′ = 22 for A6 pass
When the distance between the paper passing end and the second thermistor is long, the temperature for increasing the interval is set to 5 ° C.

For this reason, when T ₂ = 240 ° C. when the minimum size of A6 paper is passed, the maximum temperature on the heater surface is 255 ° C.
However, by switching the temperature at which the interval is switched according to the recording material size, the maximum temperature on the heater surface can be suppressed regardless of the recording material size.

Further, in addition to the recording material size information, the power supply (voltage or power supply) to the heater during the sheet feeding is detected, and the temperature T is set so that the interval becomes longer as the supply power increases.
Lower ₂ '.

This power detection takes into account the heat capacity of the recording material in addition to the size of the recording material, so that a higher effect can be obtained.

[Embodiment 5] FIG. 7 is a side view of a heater showing a fifth embodiment of the present embodiment.

In this embodiment, thermistor 5A for constant temperature control
In addition, a plurality of thermistors 5B, 5C, 5D, and 5E are provided.

In particular, they are provided corresponding to the respective recording material sizes.

Then, the detected temperatures of the thermistors 5B to 5E are set to T _{2 to} T _5, and when any one of T _{2 to} T ₅ becomes T ₂ ′ or more, the paper passing interval is lengthened.

Further, a predetermined temperature detecting element is selected by a relay according to the paper passing size (for example, a thermistor in a non-paper passing area closest to the paper passing end), and the temperature of the selected thermistor becomes T ₂ ′ or more. If so, extend the paper passing interval.

With this configuration, the maximum temperature on the heater surface can be kept low regardless of the recording material size.

In this embodiment, one thermistor is provided for each recording material size, but a plurality of thermistors may be provided.

In the embodiments described so far, the interval is changed by comparing the detected temperature of the temperature detecting element outside the paper passage area of the minimum size recording material with a predetermined temperature. An embodiment in which the interval is changed based on the difference between the temperature detected by the temperature detecting element and the temperature detected by the temperature detecting element outside the sheet passing area will be described.

[Embodiment 6] FIG. 8 shows the on-timing of the image formation start signal and the timing at which the sheet P passes through the fixing nip N when 100 continuous copies are made according to the sixth embodiment of the present invention. (When “Yes” is passing, when No is not passing).
Diagrams are also shown a graph of the detected temperature T ₁ of the thermistor 5A time detected temperature T ₂ change of the second thermistor 5B at the same time.

In this embodiment, a sheet of B4 size (width of 257 mm) weighing 80 g / m ² is passed at a speed of 100 mm / sec.

In this example, the detected temperature T ₁ of the first thermistor 5B is T ₁ ′ (for example, 225 ° C.) after the copy key is turned on until the fifth sheet passes through the fixing nip. T ₁ '' (although, T ₁ ''', for example in the present example _{T 1'<T 1 '=} 190 °) and so as, predetermined power corresponding to the value of T ₁ is supplied to the heater 1 . (However,
In this example, the reason that T ₁ = T ₁ ′ after the copy is turned on is that
About 1 second after the first sheet enters the fixing nip. However, the first sheet of fixability no practical problem), lowering the 5 th fixing setting temperature after the end T ₁ is for heating prevention device such Hitsushi BuNoboru temperature ( Since the temperature of the pressure roller and the like has been sufficiently increased by the heat treatment of the first to fifth sheets, there is no practical problem even if the temperature is lowered).

When an image formation start signal is transmitted from the MPU 19 to each part of the image forming apparatus at the same time that the copy key is pressed at time τ ₀ , the sheet feeding roller 61 starts rotating, and the sheet P is moved toward the transfer charger 34. Conveyed. At the same time τ ₀ , the rotational drive of the film 6 of the fixing device 60 and the heater 3
The energization to is started. Time τ ₁ to B4 width of the sheet P reaches the fixing nip. Time t _c (= τ ₂ −τ ₁ ) in the nip
After staying, the sheet exits the fixing nip N at time τ ₂ .

The MPU 19 issues a second image forming signal after the time t _o (for example, 5 sec) from the start of copying, and the sheet P is fed. Then, the second sheet enters the nip N at a time τ ₃ at an interval of a predetermined time t _i after the first sheet passes through the nip N.

Thereafter, the above steps are repeated until the image forming signal on the fifth sheet is turned on.

[0100] When the 5 th sheet is detected by the sheet discharge sensor (not shown) to time tau ₄ that passes through the nip, the target temperature of T ₁ is lowered 'to T _1' T ₁ 'to.

Since the heat capacity of the heater 1 is sufficiently small, the detected temperature T ₁ of the first thermistor 5 A for constant temperature control quickly decreases to T ₁ ″ by reducing the power supplied to the heater 1.

Accordingly, the detected temperature T ₂ of the second thermistor 5B also decreases.

The number of copies is still small.
₁ before and after the changeover | T ₂ -T ₁ | of the value does not change much.

The second thermistor detection temperature T ₂ is equal to the paper passing period t _c.
During the interval, the temperature rises due to the so-called non-sheet passing portion temperature rise, but falls during the interval period t _i .

However, from a macro perspective, the temperature of T ₂ gradually rises.

The temperature T _{1 in the} paper passing area is T ₁ ″ or T ₁ ′.
, The value of | T ₂ −T ₁ | (hereinafter Δ) increases.

[0107] The time before the time tau ₅ to 53 th image forming signal is generated following 54 th imaging signal after emitted _{τ 6 (τ 6 <τ 5} + t o), T 2 -T The value of ₁ reaches a predetermined value Δ ₂ (50 °).

[0108] Thus heated non-sheet passing portion temperature, the detected temperature and the detected temperature when the difference between becomes a predetermined value delta ₂ or microcomputer M of the first thermistor 5A of the second thermistor 5B
The PU 13 lengthens the interval during continuous image formation.

That is, no image forming signal is generated even if the time t _o elapses from the time τ ₅ , and the time τ _{7 obtained} by further adding the time t _i.
At (τ ₇ = τ ₆ + t _o + t _i = τ ₆ + t _c + 2t _i ), the 54th sheet image forming signal is issued. Then, the interval of the sheet P entering the fixing nip is t _i for the 1st to 53rd sheets, but it is doubled to 2t _i between the 53rd and 54th sheets. Thereafter, until the 100th image formation, the MPU1
9, the interval between the image formation start signals is t ₀ ′ = t _o +
t _i , longer than the initial. Therefore, the difference in heat radiation amount of the heat radiation amount and the first thermistor position of the second thermistor position per unit time in the heater surface is smaller than initially, thus the second thermistor temperature T ₂ is lowered, the temperature difference T ₂ - T ₁ also decreases.

Since the temperature difference between the longitudinal film, the heater, the driving roller and the like falls within a predetermined range, no running abnormality such as a deviation of the endless belt-shaped fixing film 6 occurs. Further, abnormal temperature rise in the non-sheet passing portion can be prevented.

Changing the interval based on the difference between T ₂ and T ₁ is particularly effective for an apparatus having a plurality of fixing temperatures.

As in the second embodiment, the value Δ of T ₂ −T ₁
Becomes longer than the predetermined value, the interval becomes longer and Δ decreases, and the value Δ ₂ ′ (30
° <Δ ₂₎ and comes to a shorter interval back to t _1, it is also preferable to increase the interval Once a re delta is delta ₂ or more.

Further, as shown in FIG. 9, T ₂ of the third embodiment (FIG. 6) is replaced by T ₂ −T ₁ , the interval is changed by Δ ₁ , Δ ₂ , and the apparatus is stopped at Δ _3. good.

Further, similarly to the fourth embodiment, it is preferable to change the value for switching the interval according to the recording material size and the supplied power.

Further, similarly to the fifth embodiment, a plurality of thermistors are provided outside the minimum sheet passing area in addition to the temperature control thermistor, and a temperature difference between the temperature control thermistors 5A and 5B, 5C, 5D, 5E is determined. If the temperature difference from the selected thermistor exceeds a predetermined value, the interval may be lengthened.

Although the embodiments of the present invention have been described with reference to an image heating apparatus using a fixed heater and a thin film, the present invention can be applied to other image heating apparatuses using a heating element having a small heat capacity.

[0117]

According to the present invention, it is possible to prevent the temperature in the paper non-passage area from rising without unnecessarily stopping the image heating process by merely providing the second thermistor.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a fixing device that is an image heating device according to an embodiment of the present invention.

FIG. 2 is a schematic sectional view of an image forming apparatus using the apparatus of FIG.

FIG. 3 is a side view of the heater of the embodiment shown in FIG.

FIG. 4 is a diagram showing a temperature change and a timing according to the first embodiment of the present invention.

FIG. 5 is a diagram showing a temperature change and a timing according to another embodiment of the present invention.

FIG. 6 is an explanatory view illustrating still another embodiment of the present invention.

FIG. 7 is a side view of a heater according to still another embodiment of the present invention.

FIG. 8 is a diagram showing a temperature change and a timing according to still another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heater 5A 1st temperature detecting element 5B 2nd temperature detecting element 6 Fixing film 7 Drive roller 8 Follower roller 9 Pressure roller 60 Fixing device

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-22358 (JP, A) JP-A-1-263683 (JP, A) JP-B-1-40350 (JP, B2)

Claims (2)

(57) [Claims] 1. A heating element provided in a direction intersecting with a moving direction of a recording material for heating an image on a moving recording material, and a heating element provided in a fixed minimum recording material passage area. A first thermistor for detecting the temperature of the recording medium, and energization control means for controlling energization of the heating element so that the temperature detected by the first thermistor maintains the target temperature. A second thermistor, when the second thermistor detects a predetermined first temperature during continuous image heating, the recording material feeding interval is widened, and a predetermined second temperature higher than the first temperature is detected. An image heating apparatus, wherein feeding of a recording material is stopped. 2. The apparatus according to claim 1, further comprising a film that moves in contact with the recording material, wherein an image on the recording material is heated by the heat from the heating element through the film. Item 7. The image heating device according to Item 1.